1. Field of Invention
The present invention relates to a stage for supporting, moving and positioning articles in an X-Y plane in a limited space. More particularly, the present invention relates to a cantilever stage for supporting, moving and positioning articles in an X-Y plane in a limited space such as for image-forming equipment used in manufacturing reticles, semiconductor devices and liquid crystal displays (LCD).
2. Description of the Related Art
Many devices such as reticles, semiconductor circuits and liquid crystal displays are fabricated using lithographic equipment, such as an electron beam lithography system. In the fabrication of circuits and/or liquid crystal displays, a substrate must be repeatedly and precisely positioned under the optics of a lithographic system. Such precise positioning is necessary to ensure accurate alignment of the microscopic features being formed in a new layer with other microscopic features previously formed in the layers previously formed on the substrate during the fabrication process for semiconductor circuits or liquid crystal displays.
Complex systems have been developed to precisely position an article, such as positioning a substrate or a reticle beneath the lithographic optics. A step and repeat system often uses an X-Y positioning system to position the substrate on a positioning stage beneath the lithographic equipment, expose a portion of the substrate to a pattern of light or charged particles generated by the lithographic equipment, and reposition the substrate or reticle at another location to again expose the substrate or reticle to the pattern of light or charged particles.
Many different types of positioning stage and linear motors that move the positioning stage into the desired position, such as beneath the lithographic equipment, have been developed in an attempt to provide improved accuracy of article placement. The articles being worked upon are typically supported and positioned using X-Y guides. Typically, such X-Y guides include a separate X guide assembly and a Y guide assembly, with one guide assembly mounted on and movable with the other guide assembly. Often a separate wafer stage is mounted on top of the guide assemblies. These structures comprise many components and are typically used in a wafer stepper apparatus where the alignment of an exposure field to the reticle being imaged affects the success of the circuit, i.e., the yield.
However, convention positioning stages does not provide for the moving and positioning of an article in limited space. For example, in fabricating reticles, the reticles must be carried through a narrow gap of an electron beam lithography system. Thus, conventional positioning stages cannot be used to move and position reticles in an electron beam lithography system. In addition, conventional positioning stages require additional space for counterbalance mechanism which further limits their use in limited space applications. Further, conventional positioning stages often do not shield the magnetic fields created by the moving motors from the electron beam lithography system. The magnetic fields can adversely affect the electron beam and thereby decrease the yield.
This present invention comprises a cantilever stage to support and accurately move and position articles, such as a reticle or wafer in an electron beam photolithography system. The cantilever stage generally comprises a movable member and a cantilevered support platform extending from the movable member for supporting articles to be positioned. The cantilever stage is preferably supported by and movable in an X direction along two parallel elongate guides extending through two parallel channels defined by the movable member. The two parallel elongate guides are in turn supported by a main frame.
The cantilever stage is preferably driven by two linear motors or actuators mechanically coupled to the movable member to move and position the cantilever stage in the X direction along the elongate guides. The actuators may be any suitable actuators such as electromagnetic drive motors comprising magnet tracks mounted on the main frame and cooperating with armature or coils fixed to the movable member of the cantilever stage. The coils are movable relative to the magnet tracks in the X direction upon application of an appropriate current.
Where the cantilever stage is operated at high speeds and/or high accelerations, a mechanism to cancel the reaction forces is preferably provided. Such cancellation mechanism may be achieved by providing any suitable counterbalance or reaction force cancellation device in the center of gravity or center of mass of the cantilever stage. The counterbalance device generally comprises counterbalancing mass and a linear motor disposed within a housing.
The counterbalance device is preferably provided at the center of gravity of the cantilever stage. The movable portion may define a space or region which includes the center of gravity of the cantilever stage in which the counterbalance device may be disposed. The mass of the counterbalance device counterbalancing mass is preferably approximately equal to the mass of the stage and the armature of the linear motors and may be adjustable in order to account for variances in the mass of the articles supported by the supporting platform.
Bearings such as air bearings may be provided to facilitate the movement of the cantilever stage along the elongate guides. In addition, bearings may also be provided to facilitate the movement of the counterbalancing mass relative to the remainder of the counterbalance device.
The cantilever stage may also be driven in a Y direction relative to the main frame, generally perpendicular to the X direction, by one or more actuators mechanically coupled to the elongate guides. Similar to the actuators for the X direction, the Y direction actuators may also be any suitable linear actuator. Alternatively, the cantilever stage may be driven in the Y direction by moving the main frame in the Y direction such as by actuating one or more actuators mechanically coupled to the main frame.
The cantilever positioning stage of the present invention provides a simple, effective and space-efficient method to control and align articles to be supported, moved and positioned by providing a cantilevered support platform and/or by allowing for the provision of a counterbalance device at the center of gravity of the cantilever positioning stage.
Although the present invention is described in terms moving and positioning reticles in an electron beam lithography system, the present invention can be used in any automated transport application.